1. Field of the Invention
The present invention generally relates to a method of treatment of plants. More particularly, the invention relates to an improved method of delivery of plant growth regulators.
2. Background of the Prior Art
The history of agriculture is the story of Man's attempts to modify plants and animals in order to produce more and better food. Plants (and animals) are capable of being extensively modified and Man has made use of this variability in his farming practice. In doing so he has made use of both `nature` and `nurture`--selecting and breeding from plants which have the most desirable characteristics and by cultural practices such as weeding, tilling, manuring, irrigating, pruning and disbudding he has provided the best conditions for the hereditary material of the desirable plants to realise their potential. Always of course he has been limited by the genetic makeup of the plant in question and breeding for desirable characteristics can often be a long, time-consuming, process and it may be years before the desired result is obtained. Now, however, with the introduction of chemical plant growth regulators a new dimension has been added to the possibilities of modifying plant growth and they offer the possibility of compensating for genotypic deficiencies that might take many years of breeding to alter by genetical methods.
Plant growth regulators are organic compounds, other than nutrients, that, in low concentrations, affect the morphological structure and/or physiological processes of plants. Plant hormones or phytohormones, are naturally occurring growth regulators that in low concentrations control physiological processes in plants. The synthetic growth regulators are used by Man to control such processes as fruit development, fruit thinning, defoliation, growth stimulation and retardation, rooting of cuttings and many other processes. Over the past 30 years the investigation and development of plant growth regulators has been one of the most active areas of fundamental and applied botanical research. The PANS Plant Growth Regulator Index (P. J. Kemp, 25 (2), 211 and 213) under the List of Common and Trade Names and Code Numbers has 492 entries (excluding herbicides except where these are used specifically for some growth regulatory purpose other than weedkilling).
Although ethylene has been used since the 1920's to ripen and fruit and auxins have been used to promote the rooting of cuttings, the development of plant growth regulators has been overshadowed by the development of herbicides. However, the immense amount of fundamental work that has been done on the naturally occurring auxins, the unfolding of the importance of ethylene as a plant hormone, the development of the gibberellins, the discovery of the cytokinins, the isolation of abscisic acid the synthesis of morphactins, and the development of growth retardants such as CCC (Cyclocel) have led to the recognition of the fundamental roles of the natural and practical applications of the synthetic plant growth regulators. Plant growth regulators that are in use in the United States at the present time affect a great variety of plant growth processes, including the following (some of the growth regulators in common use are in brackets): rooting of cuttings (indole-butyric acid); promotion of flowering in pineapples (1-naphthaleneacetic acid; B-hydroxyethylhydrazine; ethephon); prevention of preharvest drop of apples (NAA; daminozide); inhibition of turf growth (maleic hydrazide; mefluididediethanolamine); prevention of sprouting of potatoes (maleic hydrazide); floral induction in apple, pear, peach (succinic acid-2,2-dimethylhydrazine; 2,3,5-tri-iodobenzoic acid); early flowering of `long day` plants, e.g. lettuce, radish, mustard, dill (gibberellins); flowering of many biennials which normally require low temperatures to flower (gibberellins); improvement of yield of sugar-cane by prevention of flowering (diuron; diquat); delay in flowering in almond and peach to avoid adverse weather conditions (daminozide); induction of abscission of mature citrus fruits (cyclohexim; 5-chloro-3-methyl-4-nitro-1H-pyrazole); defoliation of cotton leaves to aid harvesting of bolls (ethephon); thinning of fruit, e.g. grapes, peaches (gibberellic acid; ethephon; 3-chlorophenoxy-.alpha.-propionamide); prevention of pre-harvest drop of citrus (2,4-dichlorophenoxyacetic acid); induction of fruit set, e.g. in tomato, squash, eggplant, fig (4-chloro-phenoxyacetic acid; 2-naphthyloxyacetic acid); increase in size and quality of grapes (gibberellins); induction of amylase in barley for malting (gibberellins); stimulation of growth of sugar-cane (gibberellins); reduction of stem length in cereals ( 2-chloroethyl trimethylammonium chloride); development of female flowers, e.g. in pumpkins (NAA; ethephon; daminozide); promotion of male flowers, e.g. in hops (gibberellins); bioregulation of plant composition, e.g. colour in citrus, sugar in sugar-cane, vitamin content in vegetables, increase in dry weight, timing of crop development, increased latex from rubber trees (various growth regulators).